1. Field of the Invention
The present invention relates to an image forming apparatus and a winding-deviation prevention method.
2. Description of the Related Art
Conventionally, there is an electrophotographic image forming apparatus. In this image forming apparatus, generally, the photosensitive drums of a development device are equally electrified and initialized, and latent images are formed on the photosensitive drums by optical writing and developed to toner images. Then, the toner images are directly or indirectly transferred onto a print target medium and fixed by a fuser.
In this image forming apparatus, when being rolled up after printing, paper (roll paper) ejected by a face-down method is reversed by a front/back reversing unit installed on the lower side of the paper ejection flow of the printer and then ejected face up. Subsequently, a tip end of the ejected paper is placed on the winding shaft of a rewinder, and then a rolling-up operation is started.
However, when the roll paper is to be rolled up, it is difficult to roll up the roll paper with both edges aligned without looseness, and therefore methods for rolling up roll paper with both edges aligned have been proposed. For example, Japanese Patent Application Laid-Open (Kokai) Publication No. 2008-074051 proposes a technique of rolling up by repeating a procedure in which a step roller (tension roller) is used to form slack of paper by self weight of the roller before rolling up, the rolling-up operation is stopped before the slack disappears, and then slack is formed again.
This technique can be relatively easily achieved, but there is a problem in that a space for providing a sensor and the step roller for continuously forming slack is required. In addition, there is a problem in that operations of keeping the rolling-up accuracy (with both edges aligned) high and achieving rolling up without looseness are easily affected by the positional accuracy of each section.
In another conventional known technique, for example, flanges (guides) conforming to the width of paper are arranged on a winding shaft, and the paper is accommodated between the guides by the guides being rotated along with the rotation of the winding shaft. However, in this conventional technique, there is a problem in that the positions of the flanges are required to be moved for a different paper width, which makes the structure complicated. In addition, there is a problem in that, when the paper is not accurately conveyed to the winding shaft, the edges of the paper are damaged by being forcibly accommodated between the guides.
In still another conventional technique, for example, fixed guides conforming to the width of paper are provided in an area on the upper side of a rolling-up flow, and the paper is positioned by being inserted therebetween and wrapped around a roll-up shaft. However, in this conventional technique, there is a problem in that unevenness occurs when an operator adjusts the guides to correspond to the paper width. In addition, a problem occurs depending on the positional accuracy of the paper. That is, when the paper is sent at a tilt with respect to the roll-up shaft, its position cannot be kept by the guides, and the rolling-up operation cannot be performed stably.
In yet another conventional technique, for example, an actuator is arranged on a roll-up shaft, an end of paper is detected by a position sensor or the like before the paper is rolled up, and the roll-up shaft is controlled such that the end of the paper is aligned, whereby the rolling-up operation is performed stably. However, in this conventional technique, there is a problem in that, since the roll diameter changes in the course of rolling up the paper into a roll shape, the sensor arrangement, the sensor type, and the structure become complicated to conform thereto, which extremely increases the cost.